Thank-you for choosing Jacks Transmissions for your transmission rebuild! We take great care to assure proper operation of the unit before it leaves our facility. We pride ourselves in our ability to modify the synchro slider timing to allow for the fastest and most accurate synchronization possible. In other words, your transmission should shift better than any other unit you have felt before! Though there is a huge amount of time spent on your transmission to assure superior synchro operation, this does not mean they can never be damaged or feel notchy if something else is wrong. The #1 reason for transmission synchro failure is due to clutch issues. Please read below for tips on how to recognize a clutch problem before it ruins your transmission. Becoming aware of clutch problems could save you thousands of dollars in transmission repairs in the future.

1)The transmission should never feel notchy or block you from a gear while shifting (some people call it ‘lockout’). If this happens, NEVER force the transmission into gear or the synchro will be ruined! This applies at any engine RPM. If it shifts smooth at low RPM, but it blocks you at high RPM, there is a clutch problem and it must be fixed immediately! When a transmission blocks you from a gear, you are experiencing what we call ‘clutch drag’. This means the clutch is not letting go of the disk fully and dragging on the assembly. An adjustment might need to be made, or the clutch could be excessively warped at the pressure plate. If the transmission won’t go into gear at all, the clutch is severely warped or broken, STOP and do not drive the car or transmission damage will occur!

2)When launching, do not ride the clutch. Riding the clutch is when someone stays in the clutch ‘friction zone’ too long and overheats the unit. When a clutch is in the friction zone, it is using friction to operate and move the car forward. If you stay in the friction zone too long, the unit will build up enough heat to damage the assembly. This can quickly warp the pressure plate and cause clutch drag, which will then cause the transmission to feel notchy when shifting.

When you launch, just give the clutch smooth and quick engagement without sitting in the friction zone. You want to stay out of the friction zone to prevent overheating, but you do not want to dump and shock the clutch either as that will break other parts. Staying in between the two can be tricky, but if you find yourself riding the clutch, let off the gas immediately and stop. Let the assembly cool for at least 15 minutes, and then try again. Do not launch over and over again, as even smooth and proper launching repeatedly will overheat the unit if not enough time is taken to allow cooling.

3)Do not shock load the clutch. Shock loading is when the driver lets the clutch go too harshly, and quickly, and allows the clutch to engage so violently that it puts a shock through the system. Shock loading while launching, or shifting, can pop the rivets of a sprung hub clutch disk and cause the clutch to drag, which will kill the transmission. Shock loading can also break Tran’s gears, CV shafts, and other drive-train components. Shock loading doesn’t make you any faster and is very harmful to many parts.

4)Become familiar with the feel of your clutch and transmission. If at any time the clutch feels different, or the transmission doesn’t shift smoothly, something is wrong. STOP and do not continue driving the car. Check for clutch drag, check the hydraulic system, or worst case, pull the clutch back out and check it too. The feel of a clutch and transmission should never change, if it does, something is wrong. Becoming familiar and aware of the feel of your clutch and transmission will help prevent costly repairs in the future. Clutches are a device that uses friction to operate, so it will warp, and it will wear out in time. It’s when the driver can notice a change, and not ignore it, that saves your transmission! Having to rebuild your transmission every time the clutch wears out, or breaks, is something that should never have to be done. If you have any questions, please feel free to contact us via phone 719-268-6011 or email This email address is being protected from spambots. You need JavaScript enabled to view it.

CLUTCH DRAG IS SERIOUS

Improper clutch adjustment, or dragging clutch assembly, will destroy your new unit. Damaged synchros due to improper clutch engagement will VOID YOUR WARRANTY!! If we receive the unit back damaged due to the clutch, we will know! 95% of all transmission failures are caused by clutch related issues. It is terribly important that the vehicle does not have clutch drag. To test is simple:

With the vehicle running, disengage the e-brake so it can roll.

Push the clutch pedal all the way to the floor and hold it there.

Turn off your launch limiter so the engine can hit the rev limiter. You MUST DO THIS!! If you do not, then there is no point in performing this test.

Shift the car into 1st gear.

Rev the engine up, while the clutch pedal is depressed all the way to the floor, until you feel the car start to move forward.

If the vehicle moves forward below the rev limiter, your clutch is dragging. Do not drive until the problem is fixed, or your synchros will be ruined! Unit will also be hard to shift, so DON’T DRIVE OR FORCE IT INTO GEAR! If everything is correct, the vehicle will not move. If the vehicle moves forward or is hard to shift, check each of the following:

Adjust the master cylinder under the dash. Video of how to do this HERE

Bleed your hydraulic clutch system and make sure you have a factory master cylinder from the dealer ONLY! Do not use generic auto parts store/eBay masters.

You may have a broken or bent clutch disk due to improper installation.

Question: Why do you need to rev the engine so high to check for clutch drag?

Answer: Clutches can drag if they are subjected to excessive engine harmonics and crankshaft torsional whip. In order to increase the engine harmonics, to test for drag, the engine RPMs need to be up high. Most engines don’t develop severe harmonics through the clutch until 5k RPM or higher.

Note: Unit is shipped empty and must be filled with oil after it is installed in the vehicle. OEM fluid is recommended for most vehicles and driving conditions.

For our Mitsubishi transmission rebuilds we recommend factory Mitsubishi transmission gear oil. More info HERE. If available, the EVO MR 6-Speed oil is the best oil to use as it has the perfect blend of friction modifiers to keep the transmission shifting smoothly and prevent gear failure. Gear oil choice is very important and varies based on preloads and synchro blocker ring design, therefore it is strongly recommended that you stick with Mitsubishi fluid for our transmissions. If you are unable to locate Mitsubishi MR 6-speed oil from the Mitsubishi dealer or us, you can use Redline MT90 (higher horsepower or race applications) gear oil. DO NOT use Synchromesh, BG Synchroshift I or II, or Royal Purple. These fluids will destroy synchros and gears and void your warranty!

WHAT IS CLUTCH DRAG AND WHY SHOULD I CARE?

When a clutch drags, it is not letting go of the disk fully which overloads the synchros and burns up the friction surfaces quickly. Synchros work by speeding up or slowing down the input shaft and clutch disk by acting like a brake. If the clutch is dragging, the synchro friction surface is trying to speed up and slow down the engine’s mass, which is impossible. The synchro will burn up, fail and the transmission has just been ruined. We believe that the synchros in all manual transmissions are brilliantly engineered and should last the life of the vehicle. If your synchros went bad and the transmission needed to be rebuilt, ask yourself why. If we claim the synchros, including the originals, should never go bad then why were yours bad? A dragging clutch is a very serious issue that is not taken seriously by the installers of your transmission and/or clutch!! It is important to be 100% sure your clutch is not dragging or you will ruin the new synchros again in short time. Synchro damage due to a dragging clutch will not be covered under our warranty. If the transmission is ruined due to a dragging clutch it will have to be rebuilt all over again. Save time and money by not burning them up and making sure the clutch is not dragging. Symptoms of a dragging clutch:

Synchros start to grind requiring a rebuild.

If the original synchros were ruined from a dragging clutch, then your new transmission will also be ruined if the issue is not fixed!

Shifting feels notchy and there is resistance while trying to shift.

If the synchro is fighting you, it means that the assembly is having a hard time synchronizing the gear. DO NOT FORCE IT INTO GEAR! A dragging clutch will make the synchros work terribly hard so shifting will not be smooth.

EVO8-10 will not go into 1st or Reverse at idle with twin disk Exedy clutch.

This is a known issue with the Exedy twin disks and is in our FAQ HERE with a fix for the problem. Again, if the transmission is forced into gear the synchros will be damaged. This problem MUST be fixed before the vehicle is driven!

I have a new clutch, so I don’t need to check for a dragging issue.

Wrong! 90% of new aftermarket clutches drag right out of the box. Many need adjustments for more throw under the dash or the pivot ball shimmed. Videos of how to do this are also on the jackstransmissions.com website.

I have a 7.25” twin disk and they don’t drag.

Wrong! Small twin disk clutches can also drag badly. Warped floaters can make them drag worse than any single disk clutch out there.

Can’t shift at high RPM.

Most clutches will drag at high RPM if there is a problem. If you miss a shift or have a hard time going into gear at high RPM, the clutch is dragging and needs to be fixed.

We cannot stress enough how important it is to be sure your clutch does not drag. Jacks Transmissions has the longest warranty in the business and we value our customers. We want our customers to have not only a long trouble free service life from their unit, but we want it to perform perfectly as well. A dragging clutch can kill your transmission within only a few shifts as the synchros are fragile. It doesn’t matter what they are made of or if they are double or triple synchro, they will be ruined if the clutch drags, period.

Also, the reverse light switch must have a crush washer or it will jam the reverse gear rail!

Please feel free to email us at This email address is being protected from spambots. You need JavaScript enabled to view it. if you have any questions or concerns over your clutch. We want to help and would be more than happy to be sure everything is right so you get the best performance possible out of your new transmission! Please review the other sheet to check for a dragging clutch as checking for a dragging clutch is simple and easy to do.

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